Questions on fibreglass techniques

I'm planning on making some modifications to my fibreglass bodywork. Nothing major, just some minor lip extensions and ribbing for locating screws etc. I’ve never worked with fibreglass before so have no idea where to start. I could start with the local supplier, but I’m sure that he deals mainly with marine applications. Should that matter? Are there pitfalls that I should know of?

The advice has always been that there is not much to it, but I’d also like to get some impressions from the home-users.

Chris, There is a lot to learn, where do I start? If you are bonding to something make sure it is roughed up by sanding & clean. Don't mix up more resin than you might need. The higher the temp. the faster it's going to harden.
Epoxy resins are the strongest & bond the best to existing composite structures, but it's the hardest to work with.
It's hard to hang fiberglass & resin in the air. I use a number of materials to make things. Example; I'll cover a piece of 1/4 plywood with aluminum foil, wax it with a good mould release wax, stik it in place with auto-body putty, do the lay up, & pull the foil covered ply off when the resin is cured. Finding the right materials is most important. Don't use epoxy resin with chopped strand mat.. use fiberglass woven cloth. 10 oz. & 6 oz. work well. Most fiberglass goods are geared to be used with polyester resins. There is a binder on these goods that disolves when polyester is introduced allowing the fibers to move freely. Epoxy doesn't do this. And use a real mould release wax, don't use 'butch's wax if you are making a small tempory mould. I could go on forever.... good luck!

Don't you also have to make sure the resin you're using in your modifications is the same as what was originally used on the shell (i.e., polyester resin on polyester-resin-based shell, epoxy on epoxy-based shell)?

Heed the safety warnings on the can about proper ventilation and breathing equipment, my uncle did a 10 minute fix on a part inside of his boat, was rushed to the hospital with 1 side of his body temporarily paralized.

Mark, I've used epoxy resins to fix many polyester structures because it bonds a little better than polyester to polyester.
I'm using vinyl ester resins now in all the lay-ups I make; FFR's Daytona Coupe, Dragon Motor Cars 'Dragon' , Lotus 23 & some aircraft parts. AND YEA! you have to follow all the safty preciousons using these materials. Most of the supply houses give out all the info you need . MSDS sheets.

Bill, I tried to send you an email but it got bounced back (I think maybe there's a missing "y" in your email address. WOuld you mind shooting me an email so I have your correct address? Thanks.

The theory that you have to use the same kind of resin to modify or repair polyester laminates as they were made with is not true. Actually, polyester bonds poorly to existing FRP materials. You are better off by far using either epoxy or vinylester resins.
Most marine stores sell comprehensive kits of compatible materials from one manufacturer. This is the best way to go. The best supplier of epoxy materials is West System, who make resin, cloth, release fabric, resin modifiers, etc etc and publish excellent and cheap literature on how to do it all. They also have numbers you can call at their factory in Michigan for help. Their stuff is used for everything from ultralights to large buildings and performs very well indeed. In vinylester, 3M is very good; they have a similar line out for marine use which again is comprehensive and includes all you're likely to need. All of these materials are better than what you would get through autobody suppliers, although they may cost a little more. It's worth it not to have to do it all twice.
I have used West epoxy for fifteen years for marine repairs and swear by it. Their stuff is wonderful.

Jim, is there a 800 number that one can call West System at? Thanks!

Mark, I just send you an email as a test.

Your first step in learning to do fiberglass
work should be to obtain the West System book for beginners. It is akin to a textbook for Epoxy Glasswork 101.
Most resins available are very similar,(Shell Petroleum makes almost all fiberglass resin available)however, Gougeon Brothers (West System) have a very thorough selection of products to make life easier for the beginner. WS is practically idiot proof. I am proof positive of this!
Be aware that WS offers fast and slow hardeners with very different pot lives, as well as numerous adhesive additives and fairing compounds for various applications.
Using the proper product for the job is critical, as using the wrong one will mean lots of extra and more difficult sanding, starting the job over from scratch, or a pot of smoking, useless goop.
Be very aware of the air temperature, as well as the temperature of the parts that you are working with. Hot days and large batches of resin don't mix!
As has been stated in an earlier post, fiberglass resin builds heat as it cures. Spread thinly, it will take far longer to cure. Globbed on thickly, it will "kick" before you want it to do so. While working with a mixture of resin and adhesive, spread it thinly on a piece of plywood or cardboard to extend the working time, as it can't build heat to accelerate the chemical reaction which cures it.
Mixing "hot" batches of resin may seem like a good idea, in order to get a job done more quickly, but this will give you a brittle repair that will crack over time. Follow the instructions carefully for resin/hardener ratios. Slower cure times make for much stronger layups/repairs.
Many types of cloth are available, chopped strand mat, woven roving, biaxial, triaxial, etc. Be sure to use the correct one, or print through can occur. You don't want your GT40 to have a hound's tooth finish!
A good mask/respirator is a must when sanding, no matter how small the job may be.
Surgical gloves, available at any pharmacy, will save your hands from acetone cleanups.
Margarine tubs or thick plastic cups make good mixing vessels.
Unfortunately, glasswork is an unforgiving science. One minor screwup will cost you dearly. Screwups equal experience, so try not to get too frustrated, as it will be a slow learning curve. It does get easier with time. (6)
There are a million little tricks to
use in different situations, some of which are covered in the WS book, but most are not.
These will become evident over time.
I could go on and on, ad infinitum. Get the West System book and study. If you still have questions, e-mail me. I have thirty years+ experience with fiberglass, and would be happy to help you if I can.

Try www.westsystem.com.

Bill

[ November 08, 2002: Message edited by: Bill Bayard ]

[ November 10, 2002: Message edited by: Bill Bayard ]

One hint that wasn't mentioned: when working on an outer body part or any piece that has been gel coated, make sure to get down to the fibreglass before bonding anything on. Bonding to the gel coat will eventually delaminate. The gel coat is saturated with wax which doesn't allow for a good bond.

Someone mentioned release agents. PVA is great stuff. If you have spray painter, you can cut way down on your useage of the material (mine is an HVLP gun and I would think this type would be best in this respect.)

Another trick, if you want a nice "dry", non-tack final finish, spray it with PVA or cover with plastic wrap. The oxygen in the air drives the hardner down away from the surface leaving the tacky feel. The PVA (poly vinyl alchohol bye-the-way) or plastic wrap will prevent the air from getting to the surface of your resin.

As mentioned, you nearly always want to roughen up the surface you are laying up on. But one extra step or the very minimum you should do to help insure a good bond, is to wipe the area down with acetone prior.

Lastly, don't be afraid of the stuff. You can always grind it back off and start over! This is one of the real beauties of composites. The biggest PITA is trying to get woven mat to stay down in a tight radius (any thing under 100º or so), especially with epoxy, as it will keep lifing up and forming a bubble. Using the tip of your paint brush in a dabbing motion helps get the bubbles out.

Be sure to wipe down all gelcoat with "wax cleaner" to remove all wax left from the wax used in the mold to "release" the glass from the mold. Tis should be done even if the glass is old. There is always traces of wax somewhere on the gel coat and this wax will get "worked i" the fiberglass as yousand. The the materials you put over this are will ot bond as well. The wax removers are availble from marine supplycompanies (West/Boats UA here). One brand is Interlux. The key is that the solvent used is fiberglass safe. Follow directions: Clean with solvent then wipe with a clean rag to remove all the wax that has been suspended so that the wax is not spread around. Good info in a book called "This old Boat", latest ed. HAve restored a 35 year old 27 ft sailboat. Now starting on a 36. cb

Some very good advice here. Bill I very much appreciate your offer of email advice. I'll probably take you up on it very soon. I had no idea that it could get this complex. It sounds like I'm getting into a very specialized area, but everyone has to start somewhere. The idiot-proof "cook book" sounds like the go for me

Although the question wasn't answered directly, it seems that there is no difference between the materials used for automotive and that used for marine applications. Am I correct here?

I'd like to ask a very specific question if I may. What would be the best approach for extending an existing ridge. The body thickness is about 6mm to 8mm in the area that I'm considering. If I manage to get halfway good at this, I might even try my new skills at tweaking the panel gaps.

Chris L, I'm sure what you mean about extending a ridge. If your going to extend an edge grind or sand it to a taper on both sides. I find it hard to hang a layup in mid air.. so you have to support it some way. If it's a curved I'll use a something that bend easilly Thin plywood, card-board anything you find suitible. Cover it with aluminum foil & wax it with a good mould relese wax. Layup one side, after it cures, tear off this support, rough up this side and layup on this side. The number of layers depends on the thickness of the original part.
As for the WEST system products; I dont use them. The resin is formulated for use with wood. The cured pruduct is too soft & flexible for layups I do. It's absolutly the best for what it was designed for. It's like sanding a rubber tire. West does make a resin system for laminating with glass. carbon & Kevlar. I believe it was used on the Voyager aircraft built by Dick & Burt Rutan. You have to call WEST and ask for the information on this rein.
Try playing around with some composite materials and you will soon develop your own techniques. Hope this a help! Bill

There isn't much difference between the composite technology used in auto and marine applications except for...
1) in marine applications, it's structural. If the hull leaks, you sink.In auto applications, if the body leaks, you just get wet.
2) marine (and aviation) laminates tend to be more robust than automotive, for similar reasons.
3) generally the stuff you buy in marine stores to fix composite structures is more expensive, with better literature (see notes above) and you get better results.
4) having used both the body shop type supplies, and the marine type stuff, I think the marine epoxy and vinylester products are much better, and now I use them to fix anything of that type, wherever it is. Good luck. Get your gloves on and get dirty, you'll learn plenty fast.

Chris,

Aluminum tape works great for retaining shapes. I've never had epoxy resin or good old polyester resin (from Home Depot) stick to it, and my glass is usually touching the side with the adhesive.

A good substitute for mold release is a watered-down solution of dishwashing liquid, applied in a couple of coats and allowed to dry, but you really only need it for epoxy. I've made some Bondo molds of my body latch recesses, and I cover them with tape, brush on the soap, then lay-on the glass. The glass pops off with minimal prying.

It's very important to make sure there are no air bubbles in the resin, and that the glass is completely wet. The tip about not adding too much hardener is a big one - you get bubbles when the reaction goes too fast. A nice trick is laying out your pieces of glass on a piece of cardboard & brushing over the entire collection until they're saturated. I've heard of folks rolling the wet glass after this to get the excess resin out (for weight).

A heat lamp or high-watt shop light is great for this time of year to help the hardening process

As for types of glass thin cloth/mesh bends around corners really easily, but there are some thinner "mat" weaves that bend easily also. Watch out for the really heavy mat, as its meant for broad, flat areas and doesn't bend.

Some of you guys might want to check out this site:

http://www.raka.com

A friend of mine with a body shop has developed a nice relationship with these guys and has gotten exactly what he needs for his applications (lots of racecars, glass, carbon, kevlar). They're very helpful, apparantly.

It takes practice - I'd play around a little off the car or on a stand-alone piece.

Good Luck

[ November 11, 2002: Message edited by: GeoffP ]

Chris , Raka epoxy! good product! It's what I use to fix aircraft parts & use if I need a structural resin. It works best with a heat cure though. I buy most of my composite supplies from Composites One Bristol, RI.
Try; www.hpcomposites.com for a ton of info.

Some really good tips here everyone.

From the experience that I've gleaned over the last couple of years I'd like to add a couple of tips to Bill's technique for extending GRP edges.


After bevelling the edges I carefully go along the edge with a knife/scalpel and dig holes into the now bevelled gelcoat for added key, as the panel bonding area is so small.

I generally use thin cereal packet type card stuck with an inch overhang and level to the panels outer skin using thin double-sided tape. I pre-laminate the card (using Spray Mount) with polyester draughting film (available from graphic suppliers) This is the best material for resin release, and if you use the shiney side the results are mirror smooth.

Extending a double-skinned panel edge is always tricky with cloth or matte as by the time you've got a couple of laminations up to the panel thickness along the edge bevel things tend to get messy with ensuing air pocket hassles. My technique which gives a more solid lamination is to use chopped matt. Usually these choppings are about 14mm long but I get a few handfuls and cut them again a few times with scissors until they are about 4mm. This allows them to lay flat and get right up tho the bevel edges etc. Once I'm happy I have enough for the job I mix them into the laminating resin and add them to the panel edge using a pointed tool (flat screwdriver tip!) in a dabbing motion. This technique is best described and "plastic spot welding" and is very handy for extending egdes by small amounts and once perfected will give you no air bubbles. Once the work is up to panel thickness and has cured you can back it up with a cloth layer.

A technique that I like to think that I discovered for filling panel surfaces is the use of colloidal silica...this came about as I found that most car fillers are useless for fairing/blending on GRP. I mix the silica powder in the resin mix until it has the consistentcy of clotted cream. Be careful with the powder as it's lighter than air and will go straight in your lungs. Once roughly mixed I pour it onto a smooth mixing surface and remix it using a filler knife/ruler/whatever. You need to work it around until the texture is super smooth. Once ready the mix can be trowelled onto the preprepared/roughened dip to be filled and then smoothed off using what ever size straight edge is appropriate. In one hit I managed to fill a dip across the entire surface of a 2ft door this way using a 3ft steel straight edge. Once cured it only needed a very light sanding to be mirror smooth and had no pinholes.

My only worry was that in theory this mix has no real strength, but the door is still perfect afer a couple of years on the road and the deepest part of the fill is about 3mm. Give this technique a go; it's awesome, and once perfected dramatically cuts down sanding/blending hassles.

BTW, epoxy to polyester=good, polyester to epoxy=bad!

Good luck,

John S.

Be careful on using silica. It makes resin very brittle used in thick and thin sections, but gives the resin good impact resistance. Used in too thick of a mass, it will crack from it's own heat. I'v been using it for many years mixed with gelcoat to do repaires in gelcoat. Most forulators use a high shear mixer to mix it into the resin, but mixing by hand just takes a little work to get it smooth.

Bill,

Good points...boy, I wished I'd found this forum a few years back! I spent a lot of time faffing with the stuff on various test laminations of GRP until I was happy that the evil formula would work and stay in one piece when I flexed it.

Most of the people around here that have any knowledge of GRP are boatbuilders (River Thames) and they only seem to use the stuff for making radiused fairing fillets around keels etc.

Just for the record:
www.pbase.com/image/4950253

John S.